AN INVESTIGATION OF HYDROGEN DIFFUSION IN NANOCRYSTALLINE PD BY NEUTRON SPECTROSCOPY

The diffusion of H interstitials in nanocrystalline Pd was investigate d by neutron spectroscopy (temperatures of 288 and 300 K, grain diamet ers between 7 and 25 nm, H concentrations of 2.9 and 3.7 at.%). The ex periments indicate that a high fraction of the dissolved H is located in grain boundaries (this agrees with previous studies). They show fur ther that the H atoms in the grain boundaries perform a diffusion proc ess which (i) is partially locally restricted and (ii) exhibits jump r ates that are up to a factor similar to 100 higher than those of diffu sion within the grains.